Radio amplifier with arrangement for electric-phonograph reproduction



Apxrfifl M, ma P. MUELLER ,0

RADIO ABZPLIFIBR WITH ARRANGEMENT FOR ELECTRIC PHONbGRAPH REPRODUCTION Filed April 1, 1955 INVENTOR PAUL All/ELLE? ATTORNEY Patented Apr. 14, 1936 UNITED STATES RADIO AMPLIFIER. WITH ARRANGEMENT FOR ELECTBIIC-PHONOGRAPH REPRO- DUCTION Paul Mueller, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application April 1, 1933, Serial No. 663,921 In Germany April 6, 1932 7 Claims.

The present invention relates to an improvement in radio receivers with volume control arrangement also adapted for the purpose of electric phonograph reproduction. In radio receivers the connection to phonograph reproduction was hitherto accomplished in such manner that by operating the switch for the wave range selection it is possible to receive long waves in the one position of the switch, short waves in the other position of the switch and the phonograph reproduction in a third position. Such arrangements have the disadvantage that disturbing noises are received by the antenna and thus reproduced since in the case of phonograph reproduction the high frequency amplifiers are also in operation.

According to the present invention, in receivers provided with a shaft or knob for volume control whereby the preliminary tubes are affected, the phonograph switch is combined with the volume control knob or shaft.

An object of the invention, therefore, is toprovide a single operating means for operating a phonograph switch and for controlling the radio frequency voltage applied to the input circuit of a detector.

A further object of the invention is to progressively reduce the amplification of a stage of radio frequency of a radio receiver as a cooperating phonograph switch is adjusted towards its closed position. This is preferably done, according to my invention, by increasing the bias voltage applied to the grid of the radio frequency amplifier. I further prefer to open the amplifier grid circuit when the phonograph switch is fully closed.

An embodiment of the invention is shown in the accompanying drawing in which:

Fig. 1 shows a schematic circuit diagram of the preferred control means; and,

Fig. 2 shows an arrangement of rheostat and switch embodying the invention.

Referring to Fig. 1, the primary coil I of the antenna circuit A is connected to the grid circuit of the radio frequency amplifier H by the secondary coil 2, which may be tuned to the signal frequency by variable condenser 3. The grid 4 of tube H may be connected to its cathode 5 through any desired portion of resistor or potentiometer 6 and an adjustable contact arm 1. A suitable battery 0 is connected across 6 to provide the desired bias to grid 4, so that when arm 1 is at the left hand end of 6 the large negative bias given to grid 4 is such as to reduce the amplification of the signal by tube H to a very low value, so that it will have substantially no effect on the input circuit of detector tube G.

The plate circuit of H may be connected to the grid circuit of detector tube G by the transformer T whose secondary 8 may be tuned to the signal frequency by a variable condenser 9. As shown the detector is of the grid leak type having a grid leak, condenser combination H1 in its grid circuit. The audio frequency output of the detector may be amplified by a vacuum tube amplifier K in whose plate circuit the loudspeaker L may be connected in any known manner. The audio frequency currents generated by a phonograph pick-up l5 may be impressed across the grid l6 and cathode I! of detector G by the primary I4 and secondary l3 of an audio transformer S, the secondary terminals l8 of which may be conductively connected to Hi and I! by leads II and I2. A switch comprising the movable contact arm l9 and contact 20 is preferably connected in lead II to selectively connect the phonograph pick-up to the grid and cathode of the detector, which serves as an audio amplifier for the phonograph pick-up.

As shown in Fig. 2 the switch arm l9 and contact arm 1 may be mounted on a shaft 2| of insulating material at such relative locations that arm l9 does not make contact with 20 until arm 1 is near the negative end of potentiometer 6 or, if desired, until arm 1 has left the upper end of 6 at which time the grid circuit of tube H will be open and no radio signal energy will be impressed on the grid circuit of the detector as the phonograph switch l9 makes connection. A usual type of control knob 22 may be provided to operate shaft 2|.

Having described my invention, what I claim is:

1. In combination, a high frequency amplifier having a grid circuit including a control grid and cathode, and an output circuit, a resistor having one end connected to said control grid, means for causing a uni-directional current to flow through said resistor, a contact arm adjustable along said resistor and connected to said grid circuit, a vacuum tube amplifier having a grid circuit coupled to said output circuit and including a control grid and cathode, a source of low frequency signals, a line connecting said source to the grid and cathode of said last named amplifier, a switch having a single movable contact arm connected in said line and a single control shaft on which said first mentioned contact arm and said switch arm are mounted.

2. In a radio phonograph device, a radio frequency amplifier having a grid circuit and a plate circuit, means for impressing radio signal currents on said grid circuit, a detector coupled to said plate circuit and having a grid circuit including a control grid and cathode, a source of low frequency signals, a line connecting said source with said detector grid and cathode, a. switch in said line and means for decreasing the amplification factor of said radio frequency amplifier as said switch is adjusted toward its closed position.

3. In combination, a radio frequency amplifier having a grid circuit including a control grid, and an output circuit, means for controlling the bias on said control grid, a vacuum tube amplifier having a grid circuit coupled to said output circuit and including a control grid and cathode, a source of low frequency signals, a line connecting said source to the grid and cathode of said last named amplifier, switching means in said line and means to adjust said bias control means to increase the negative bias on said control grid as said switching means is adjusted to its closed position. 7

4. The combination of the preceding cl-airn in which a single operating member is arranged to operate said bias control means and said switching means.

5. In combination, a high frequency amplifier having a grid circuit including a control grid and cathode, and an output circuit, a potentiometer connected to said cathode and having an adjustable contact arm, a direct current voltage source having its terminals connected to the ends of said potentiometer, a vacuum tube amplifier hair'- ing a grid circuit coupled to said output circuit and including a control grid and cathode, a source of low frequency signals, a line connecting said source to the grid and cathode of said last named amplifier, a switching device having a contact arm in said line and a common shaft for operating said contact arm and the adjustable contact of said potentiometer.

6. The combination defined in the preceding claim in which the contact arm of said switching device and the adjustable contact of said potentiometer are both mounted on said common shaft,

7. In combination, a radio frequency amplifier having a grid circuit including a cathode and control grid, and an output circuit, a resistor having one end permanently connected to said cathode, means for causing a direct current to pass through said resistor, a contact arm permanently connected to said control grid and adjustable along said resistor, a vacuum tube amplifier having a grid circuit coupled to said output circuit and including a control grid and cathode, a phonograph pick-up, a line connecting said pick-up to the grid and cathode of said last named amplifier, a switch having a movable contact arm connected in said line and a single operating means arranged to move said contact arm past the low potential end of said resistor and to subsequently cause said movable contact to close said switch.

PAUL MUELLER. 

